Electrical reactance, and method and apparatus



, July 10,1928. 1,676,745

G. W. PICKARD ELECTRICAL REAGTANCE, AND METHOD AND APPARATUS Filed Sept. 24, 1924 5 Sheets-Sheet l ATTORNEY July 10, 1928. 1,676,745

' G. w. PICKARD ELECTRICAL REACTANCE, AND METHOD AND APPARATUS 7 Filed Sept. 24, 1924 3 Sheets-Sheet 2 INVENTOR ELECTRICAL HEACTANGE, AND METHOD AND APPARATUS Filed Sept. 24, 1924 3 Sheets-Sheet 5 v B f I L\ if i -H l W J! A .l 6; H ATTOR EY Patented July 10, 1928.

- UNITED STATES PATENT OFFICE.

GREENLEAF WHITTIER PICKARD, OF NEWTON CENTER, MASSACHUSETTS, ASSIGNOR TO WIRELESS SPECIALTY APPARATUS COMPANY, OF BOSTON, MASSACHUSETTS, A

CORPORATION OF NEW YORK.

ELECTRICAL REACTANCE, AND METHOD AND APPARATUS.

Application filed September 24, 1924. Serial No. 789,517.

This invention relates to electrical reactances, and particularly to such reactances as those high resistances and small capacities which are employed respectively as grid leaks and grid condensers 111 radio receiving apparatus. I

The object of the invention is to lmprove the construction of such devices, particularly as to scaling them from the atmosphere and providing convenient circuit terminals which are in good electrical contact with the reactance members themselves.

The invention consists of the methods, apparatus and product described herem and shown in the drawings, of which Figs. 1-6 show one process, apparatus and product, Fig, 7-9 show a modified form of apparatus, Fig. 10 a combination reactance member (the apparatus and methods hereof being adapted to be used in connection wlthvarious forms of product), and Figs. 1120 show another method and yet another apparatus, illustrated in connection with a combination reactance similar to that of Fig. 10.

Of Figs. 16, Fig. 1 is a perspective of an element which is to serve as a resistance member; Fig. 2 is a perspective of an enclosure for said resistance member; Fig. 3 is a perspective showing a permissible treatment of the member of Fig. 1; Fig. 4 is a perspective, partly in section, of a mold which can be used to effectuate the method hereof; Fig. 5 is a view similar to Fig. 4, showing in place in the mold several assemblies of the devices of Figs. 1 and 2; and

Fig. 6 is a View similar to Figs. 4 and 5 showing the assemblies completed in accordance with the invention.

The drawings are greatly enlarged for clearness. In Fig. Ithe member P is a narrow comparatively thin sheet of material impregnatable with a fluid resistance; and may be a cardboard-like material, such as bristol board, or any thin pasteboard 01 more or less thick paper. The element GT of Fig. 2 is a tube of insulating material,

preferably glass.

In Fig. 8 is shown a portion of a tray D containing fluid resistance material such as Higginss Eternal Carbon Ink. In this is dipped the impregnata-ble material P of Fig. 1 to produce the resistance element GL, as a high resistance grid leak; or the impregnatable material may be painted with the resistance material. After being dipped, it is dried to obtain a deposit. For lower .resistances desired, the process of dipboth sides of the sheet may be painted. It

is practicable to paint the paper in a large sheet by means ofv a brush, the ink being applied with a heavy coat and permitted to dry. After drying, the paper should not be bent or wrinkled, for that is liable to alter the resistance. The large sheet then is cut lnto strips.

In Fig. 4 is shown a metal mold consisting of two parts U U joined vertically, and provided with spaces receiving molten metal WM, the spaces or depressions being shaped in accord with the desired configuration of the external circuit terminals of the device, as shown at the top of Fig. 6. These depressions are filled with a molten metal such as Woods metal, which may be of composition resulting in melting at about the boiling point of water. Metals of higher meltin point may be used, such as solder; but alFoys such as the well-known Woods mctalare preferred because their lower boiling point avoids cracking of glass tube GT or c1arr1ng of the ends of resistance sheet GL. VVoods metal is preferred for use herein which has .a compositionresulting in its melting at about 80 (1, 20 below the boiling point of water. Such metals as are used herein possess the characteristic of expanding upon solidification.

As shown in Fig. 5, the resistance GL of Fig. 3 and the glass tube GT of Fig. 2 are assembled in pairs, the former within, the latter, and inserted and held in the molten metal WM in separable mold U U adjacent ends of the two elements projecting down into the molten metal, where they are kept until the fluid metal solidifies sufliciently to permit separation of the'mold parts from one another. As the casting-metal cools, it expands, and sticks to the mold-metal as well as tightly gripping the end of the glasstube and the end of reactance GL. The split PSI ' the parts, tightly grip t the bottomof Fig. 5 and at the top of mold U U permits mold-separation, so as to permit prompt removal of the device from the mold without liability of 1pulling from the seal WM, either of the e ements embedded therein. In Fig. 6, the reactance assemblies have been inverted from their positions in Fig. 5, the result of the step "of Fig. 5bein'g shown at the top of Fig. 6, in the form of the external circuit terminals WM which surround the outside of glass tube GT near its upper end, close the open end of the tube, and, b expansion against he tube and the end of resistance element GL, holding the tube permanently in assembly, and' forming good electrical connection between ,the metal WM and the resistance-deposit on the resistance element GL, Also the metal WVM hermetically seals the interior of glass tube GT, preventing access of moisture from the external atmosphere to the resistance element GL and thereby preserving uniform resistance. In Fig. 6 the opposite ends are being sealed, exactly like the first end shown at Fig. 6. While the process of Figs. 4.-6 1s a practicable form, yet it involves the manual holding of the reactance and enclosing tube in position in molten metal \VM until substantial solidification of the latter. Figs. 7-9 show a modified form of molding apparatus which avoids manipulation of the device after its end is placed in the molten metal in the mold, and during solidification of the casting-metal. Fig. 7 is an elevation of the molding apparatus, partly in section; Fig. 8 is a portion thereof showing'the metal end seal in elevation and Fig. 9 is a plan view of the top support 1 of Fig. 7

which is a spring clamp which grips the glass tube GT. In Fig. 7 the apparatus includes a suitable base on which the parts are mounted, including a standard S for the I spring clip 1. Also bolts B are screwed in the base and are screw-threaded at their upper ends to engage ,in upper mold part V. On the base also is secured lower mold part U which has a depression U at its top shaped to the desired configuration of the end of the metal seal. On top of upper mold member V is mounted an auxiliary member U by screws A. Parts U and V have a central perforation receiving the upper end of lower mold member V In operation, the glass tube, with resistance element GL inside it, and with its ends projecting beyond the open ends of the tube (as shown also in Figs. 5 and 6), is placed so that the arms of s ring clip 1 grip the outside of one end of the tube, the lower end of the tube, and the lower end of GL lying in the molten metal WM in the depression or casting space in the mold members U and U The tube GT, being by far the heavier element,

is thus supported in proper position for the to the outside of the metal molds.

cast-sealing of its lower end. Resistance element G may be held in place by hand for a moment until the molten metal hardens suflicient to sustain its light weight; or inside the tube may be placed perforated disks like Fig. 18 to be described, for the purpose of su porting GL to the interior of the tube and olding it in place without manipulation during solidification of the casting metal. In the cases of any of the metal molds herein, solidification of the casting metal may be facilitated by'the application of a cooling medium such as water or air, In Fi 7, after the molten metal WM has solidifie being then adherent to the inner walls of the metal .mold members, one mold member is moved relative to the other in order to loosen the casting from the mold walls and facilitate the prompt removal of the reactance device without liability of se arating Figs. 46. In Fig.7, the upper mold member is forced down manually against helical springs 2 surrounding bolts B, so that said upper mold member assumes the position showni-n dotted lines where the top of part U is below the sides of end casting WM; whereupon the casting readily may be removed from the mold. Wing nuts W engage the upper ends of bolts B above part V of the upper mold member, and determine the upper or operative position of the upper mold member. Upon manual release of the upper mold member, springs 2 force it up against the wing nuts W to operative osition. Fig. 8 shows the resulting casting WM at the top of the apparatus, the resistance element having been inverted from the position shown in Fig. 7 for the purpose of casting the circuit terminal about the other end of the device which is the upper end shown in Fig. 7. On the base B may be mounted a plurality of molds like those shown in Figs. 7-8, to facilitate quantity production. Although in Fig. 9 only the glass tube GT is shown in spring clip 1, it is to be understood that the resistance element GL is to be placed down inside the vertical tube to'project the desired distance into the molten. metal VM, so that the two conducting ends of the resistance element GL project beyond the respective ends of the tube in order to facilitate the gripping of said conducting ends by the casting metal to form good electrical contact therewith. In Fig. 7 is illustrated the fact that the insulating tube GT may house or enclose a reactance C other. than the resistance GL and C, or two reactances including GL.

-sheets P P sheet condenser C, with projecting terminal foils F F this condenser being arran ed and connected in parallel with reslstance L, the latter permissively being provided with metal spring clamps CC at its ends; and n Fig. 7 said double reactance C and GL shown as in place inside tube GT.

Figs. 11-17. illustrate the manufacture of combined resistance and capacity reactances similar to that of Fig. 10. Figfll 1s an exploded View of the condenser stack before rolling into cylindrical form. It may consist of alternately disposed foil sheets F F? and paper or other flexible dielectric The arrangement of these sheets in the stack is as shown, so that upon rolling the stack from right to left as indicated in Fig. 11, the u =per foil F will be the inside of the cylin er and the lower or dielectric sheet P will bethe outside of the roll as shown in Fig. 12; the foils F and F projecting from oppositesides of the stack, constituting projecting terminals from the ends of the roll, and the whole constituting the roll condenser C of Fig. 12. This condenser m'ay have a capacity of .0003 mfd.; the paper sheets P P being approximately four inches long by an inch and a quarter wide; and the foil sheets F, F being about three inches long by one inch wide; the width of the sheets in each case being lengthwise of the rolled condenser. Figs. 13 and 13 are an elevation and section respectively of a paper or other impregnatable sheet P; and this as shown in Figs. 14 and 14' has been treated as by dipping or painting in -or w'th a fluid resistance material, so as to constitute a resistance element.

In Fig. 15- the condenser roll P of Fig. 12 has been flattened on one side, and the resistance element G of Fig. 14 has been laid alongside it against said flattened side, the two having substant'ally the same length so that the conducting ends of resistance GL lie alongside the projecting foils F and F of condenser C. Fig. 16 shows a tray D in section containing a fluid in which are dipped respectively the ends of the combined impedance of Fig. 15. The upper end of this combination in Fig. 16 is shown as having a coating (i as the result of dipping in the fluid G in tray D the lower end of the combined impedance being under treatment in Fig. 16. Th s coating G is of conducting material of lower resistance than that with which the sheet has been impregnated in Fig. 14. The fluid intray D may consist of powdered graphite made into a rather thick pa'nt by water glass. Or the material G may be a bronze paint applied with a brush and containing bronze powder with amyl acetate with a little collodion in solution to constitute the whole as a lacquer. In Fig. 17 the combfned impedance of Fig. 15, provided with the end coatings G of Fig. '16,

is shown as placed inside a glass tube GT, the ends of the reactance being supported ininsulating or other disks K held inside the tube and having perforations H (Fig. 18) to permit the passage of the ends of the eactance which are tightly fitted against the walls of openings H under the two disks near the ends of the device. The yielding nature of 'the paper of Figs. 13-14, and of the projecting foils F F permits this fitt ng in disks K.

The coated ends G have the function of ensuring good electrical contact between the ends of the impedance and the exterior circuit terminals WM of Figs. 6 and 8, additional to the effect of the expansion of the metal, upon solidification, against these ends of-the' reactance; and coatings G may be several tmils thick, constituting bulges of irregular contour on the ends as a means of increasing the grip of metal terminals W'M on the ends of the impedance. These coat.- ings G may be applied to any individual electrical reactance, as either the simple resistance sheet of Figs. 16. or to the condenser C of Figs. 10-12; and when used with the resistance GL alone, the coatings G may replace the metal clamps or clips CC of Fig. 10. The disks K of Fig. 17 serve to support the reactance inside the surrounding tube during the casting operation as in Figs. 46 or Figs. 79; and these disks K may be employed for a single reactance alone, as the resistance GL of Figs. 4-6, or the condenser C of Figs. 7, 10-12, as well as in the case of the combined impedance of Figs. 15-17.

In Fig. 20 is shown a preferred form of apparatus for sealing the ends of the impedance device with the external metal circuit terminals. This apparatus is useful inv the case of production of the devices one by one, but is particularly advantageous for quantity production. In the method which is executed by this apparatus, the assembly of Fig. 17, including glass tube GT, a suitable electrical reactance such as condenser C, and the disks K, is placed in horizontal position. Here, instead of the reactance device being placed with its end in a mold wherein the upper surface of the molten metal is exposed, the ends of the horizontal reactance device are located in casting spaces formed in the two parts of a vertically split mold U U and the molten metal possessing expansibility on solidification, is poured into gates L L V-shaped and communicating by small openings T with the respective casting spaces. The insulating tube GT is shown as cut away at the right. Fig. 20, to show the casting operation. Here, the disk K serves as a barrier to the flow of molten metal from the casting space to the interior of the tube. and around the react ance between the two disks atthe opposite ends of the tube. Also the flow of the molten metal from the casting space too far around the outside of insulating tube GT, is barred by barriers shown in Fig. 19. There are two of these barriers T T Fig. 20, one at the left and one at the right. Each barrier is formed in two parts (Fig. 19) in order to permit removal of the completed reactance device from the mold. Each of the two parts of each barrier is formed with a semicircular groove 0 which register with one another and permitthe barrier (Fig. 20) to closely surround the glass tube and permit the formation of casting-portion Z around the outside of the end of insulating tube GT. The two parts U, U of the mold are formed so that when assembled they constitute a channel J, J the floor of which serves as a support for the tubes GT in casting position. In assembling the mold, the lower part T of the left-hand vertical barrier, is placed in the position shown in Fig. 10, one set of ends of the assemblies of Fig. 17 are inserted in the casting spaces of, say, the left-hand mold member U, the left-hand portions of tubes GT resting in the grooves in said lower member T Thereupon the right-hand mold part U is moved toward the left-hand part, the lower member T of the right-hand barrier being in the position shown in Fig. 20, so that the right-hand portion of insulating tube GT rests in the groove thereof; then the two mold parts are brought into contact with one another, guided by pointed pins E, and the right-hand ends of the reactance assemblies are located in proper position in the casting spaces in the right-hand mold member U Then the upper parts T of the left-hand and right-hand barriers are placed in the positions shown in Fig. 20 on top of tubes GT. In this situation, the parts are in position to permit the molten metal to be poured into the gates L L which then flows through small openings T into the casting spaces for the respective terminal casting-seals. The metal WM, as in the preceding forms, upon solidification expands against the outside of enclosing tubes GT, against the projecting conductingends of the enclosed reactance, and against the metal walls of the mold, adhering to the latter. Upon suflicient solidification of the casting metal, the molds are separated by relative movement as by the withdrawal to the right of right-hand mold part U so as to separate from the surfaces of the metal mold the solidified casting metal adherent thereto, preliminary to the complete removal of the completed reactance device from the molding apparatus. The withdrawal to the right Y of right-hand mold member U exposes the ends of the plurality of reactance devices, leaving theupper art T of the right-hand barrier on top of t e plurality of insulating tubes GT. Thereupon the several completed reactance devices may be withdrawn to the right from out of left-hand mold member U moving the two parts of left-hand barrier T T from their positions adjacent said left-hand mold part. In the case of each mold half, the small openings T between the gate and the molding spaces are such as readily to permit breakage of the gate metal from the molded terminals at the time respectively of the moving to the right of right-hand mold member U and the moving to the right of the several completed reactance devices from out of the left-hand mold member U In Fig. 20, the line of separation between the two mold parts U, U is transverse to the length of the tube, as in Fig. 7; and, if desired, in the apparatus of Fig. 20, moldportions Z (or at least one of them) may be formed integral with upper parts T of the barrier of Fig. 19, and, like T removable, to permit the completed reactances to be lifted out of the mold after more or less separation of mold parts U and U The invention'not only provides a practical and low-cost combination seal and external circuit terminal for a tube enclosed electrical reactance, wherein the seal holds J in permanent assembly a minimum number of parts; but it provides apparatus and processes for producing such sealed reactances in quantity at low factory cost. While the various processes and apparatus disclosed are prac tical, yet those of Fig. 20 are especially advantageous in freeing the process of all handling or manual supporting of the parts of the reactance assembly during the casting process.

The invention involving broadly the inclusion of condenser in the insulating tube and disclosed in the copending application of Bailey, S. N. 740,925 filed 1 October, 1924 wasmade by said Bailey and not by me. But my invention hereof includes the method of Fig. 20 and related figures hereof.

I particularly point out and distinctly claim the part, improvement, or combination which I claim as my invention or discovery, as follows:

1. An electrical impedance which comprises an insulating tube, an impedance memer enclosed therein, insulating disks inside the tube and having holes through which extend conducting ends of the impedance; and external terminals consisting of metal which expands upon solidification around the outside of the tube and the conducting ends of the impedance which extend beyond said disks, forming a hermetic seal for the impedance between the disks and permanently holding the parts in assembly.

2. The method consisting in placing an electrical device in an open-ended tube of insulating mater al, with t e nducting W'- minals of the device located approximately at the open ends of the tube; inserting perforated disks in the ends of the tube and over the terminals of the device, locating the disks inwardly of the ends of the tube and the terminals of the device; embedding the ends of said assembled structure exposed from said disks in molten metal of low melting point which expands upon solidification; and allowing solidification of said expanding metal portions thereby causing the latter to grip the terminals of the electrical device in good electrical contact.

GREENLEAF WHITTIER PICKARD. 

